Steel having improved free-cutting properties

ABSTRACT

A MACHINE STRUCTURE STEEL HAVING SUPERIOR FREE-CUTTING PROPERTIES, YIELD STRENGTH AND TENSILE STRENGTH AND COMPRISING THE ADDITION OF 0.002% TO 0.02% CA, 0.005% TO 0.04% SOL. AL. AND 0.005% TO 0.1% NB AND/OR V, TO KNOWN COMPOSITION CONTAINED IN ORDINARY STEEL.

Jan. 29, TOHRU 'MlMINO ETAL. STEEL HAVING IMPROVED FREE-CUTTINGPROPERTIES 3 Sheets-Sheet 1 Filed June 30, 1971 N m a l MA .1 fin mww 1mm% I 0 a 0 5 m m 0 m 0 w 0 O. O. O. O O O 0 0.002. 0.000 0.010 0.014 aW) HGJ BASIC STEEL -14 I6 CUTTING TIMEJ, (MIN) FIG-.2

O24-68IOI2 INVENTORS TOHRU M HVHNO SHUUROKU NARA YOSHIO MIYASHITAKATSUHIKO NISHIKAWA Ca BY l 1 3 ,TORNEY Jan. 29, 19 74 TQHRU MIMINIOEFAL 3,788,843

STEEL HAVING IMPROVED FREE-CUTTING PROPERTIES Filed June so, 1971 3Sheets-Sheet 5 33 5g; 20 BASIC g STEEL LLU 6 I l0- w FREE" CUTTI N6STEEL\ O l 0 2 4 6 8 IO I2 [4 l6 CUTTING TIME ,,T,(M|N) CUTTING TIME110mm.

0.025 9,05 g 0 sl0 TOHRU MIMINO I? I D 5 INVENTORS ATTORNEY ToHRu MIMINOE L 3,788,843

STEEL HAVING IMPROVED FREE-CUTTING PROPERTIES Jan. 29, 1974 Filed June30, 1971 3 Sheets-Sheet :6

l-IARGE s) HARGES) mi? wu 92m 5 zom/mi mo Emma CUTTING TIME TWIN) FIG 6o N E V m N m T E SE V H T TWS O 1 m 6 HM m m W mJ L 1' W .E 4 E C S. Er2 7 m o G I 8 F. 6 CL E S AW 4 BS 2 m o O m 2 w. 0

A3; S5 wi E zommfio 1E5 TOHRU MIMINO SHUUROKU NARA YOSHIO MIYASHITAKATSUHI KO NlSHlKA/VA ATTORNEY United "States Patent Int. Cl. C22c37/10, 39/02 US. Cl. 75-124 4 Claims ABSTRACT OF THE DISCLOSURE Amachine structure steel having superior free-cutting properties, yieldstrength and tensile strength and comprising the addition of 0.002% to0.02% Ca, 0.005% to 0.04% Sol. Al. and 0.005% to 0.1% Nb and/or V, toknown composition contained in ordinary steel.

BACKGROUND OF THE INVENTION This invention relates to steel compositionsand more particularly to steels having improved free-cuttmg properties.

Generally, the following characteristics should be considered inevaluating the free-cutting properties of a machine structural steel:

(1) useful life of a tool employing the steel, (2) roughness of amachined surface,

(3) cutting resistance,

(4) crushing property of a chip.

It is, however, customary that among the aforementioned propertiesuseful life is stressed most often. Accordingly, steel displayingexcellent abrasion resistance may be recognized as the best suited forcutting jobs, such as when used in a tool.

Steel, which may be, for example, a sulphur (S) freecutting steelcontaining about 0.3% S, a lead (Pb) freecutting steel containing 0.15%to 0.3% Pb, or a sulphurlead free-cutting steel containing both S and Pbhave been employed for the above purpose. It is however, wellknown thatthe utility of these steels is limited by reason of certain commondefects existing in these steels, such as that such steels are confinedto cutting jobs performed at low speeds.

The calcium (Ca) free-cutting steel was thus developed. This steelcontains more than 0.002% Ca and an adjusted amount of S01. Al. Itshould be noted at this point that the percents recited herein refers topercentage by weight. This steels ability to be machined is improvedover that discussed above, to be suitable for cutting work at highspeeds. It was found however that the Ca free-cutting steel had largedispersions of abrasion amount when employed in a tool and hence thedepth of abrasion was close to that of ordinary steel. There was onlyslight possibility that such dispersion could be reduced. The relativeamounts of Ca and S01. A1. are difiicult to adjust to the most suitablelevel, with concurrent stability.

Therefore, a calcium-sulphur free-cutting steel was developed,comprising the addition of S to steel, in order to remove the foregoingdefect. The abrasion amount of a tool employing Ca-S free-cutting steel,is reduced to smaller dispersions and less depth. However, this steel isstill deficient in certain mechanical properties.

Thus, there is a great need today for steels which have improvedmechanical properties and are stable and have excellent free-cuttingproperties at high speeds and may be used for example in cementedcarbide tools for cutting work.

SUMMARY OF THE. INVENTION Accordingly, an object of this invention is toprovide a machine structure steel stably displaying excellentfreecutting properties with the least abrasion amount when employed in atool at high speeds.

Another object of this invention is to provide a steel which reduces theworking cost when used in cemented carbide tools.

A further object of this invention is to provide a steel possessingbetter mechanical properties and better freecutting properties thanthose of known steels.

The foregoing and other objects and features of this invention areattained by a steel comprising the addition of 0.002% to 0.02% Ca,0.005% to 0.04% Sol. Al. and 0.005% to 0.1% niobium (Nb) and/or vanadium(V) to the known compositions of ordinary machine structure steels.

BRIEF DESCRIPTION OF DRAWING FIG. 1 is a graph depicting the relationbetween Ca percent and S01. Al. percent in a known Ca free-cutting steeland the resulting influence on abrasion of a tool employing such steel;

FIG. 2 is a graph depicting how the abrasion amount of a tool using aknown Ca free-cutting steel is changed with passage of cutting time, incomparison with that of basic steel;

FIG. 3, is a diagram depicting the relation between Ca percent and S01.Al. percent as shown in FIG. 1 plotting with actual samples;

FIG. 4 is a graph depicting how the abrasion amount of a tool using aknown Ca-S free-cutting steel is changed with passage of cutting time,in comparison with basic steel;

FIG. 5 is a diagram depicting the relation between Ca percent and S01.Al. percent in a Ca-S steel as plotted with actual samples;

FIG. 6 is a graph depicting the abrasion amount of a tool using thesteel of this invention as changed with passage of cutting time, andplotted using a comparison with each of several steels.

FIG. 7 depicts a graph showing how the abrasion amount of a tool usingthe steel of this invention is changed with the passage of cutting time,in comparison with other steels.

DETAILED DESCRIPTION OF HREFERR'ED EMBODIMENT Turning now to FIG. 1there is depicted a graph showing the relation between Sol. Al percentand Ca percent in a Ca free-cutting steel. This steel was produced byadding Ca to the basic steel discussed above and to be discussed ingreater detail hereinbelow. There is depicted a zone showing goodabrasion resistance. Experiments have shown that Ca free-cutting steelhas large dispersions of amount of dispersive abrasion. FIG. 3 depictsthe relation as plotted with actual data from actual samples.

FIGS. 2 and 3 depict the amount of abrasion depth as measured againstcutting time. It can be readily understood that the increase of depth ofabrasion with time is not desirable.

Turning then to FIG. 5, there is depicted a plot of data obtained withactual examples of Ca-S free-cutting steel, measuring Sol. Al percentagainst Ca percent. The cutting time was 10 minutes. In FIG. 4, there isdepicted the depth of abrasion as measured against time for a Ca-Sfreecutting steel. The depth does not increase in any substantial mannerwith passage of cutting time. This is probably 3 due to the addition ofmore than 0.04% S to the Ca steel discussed above with reference to FIG.1.

It was found that despite the advantageous small dispersions and nosubstantial increase in depth of abrasion with passage of time, certainmechanical properties are deficient. The following Table I showsmechanical properties of the above Ca-S free-cutting steel in comparisonwith that of Ca free-cutting steel.

substantially reduce the abrasive qualities of a tool using theresulting steel. When the S01. Al. content is more than 0.04% theabrasion resistance of the tool is lowered to a considerable degree andwhen the S01. Al. content is less than 0.005 deoxidation and grain sizeof the resulting steel will be difiicult to control. More than 0.1% Nbor V or Nb and V brings little change of the abrasion resistance of atool using the resulting steel and brings only added TABLE I YieldTensile Elonga- Dlrection of test point, strength tion Kind of steelpiece kgJmmJ kg.lmm. percent Heat treatment Longitudinal (L) 42. 62. 533 C8 free-cutti g Steel ..-{E t 1 2g Norinaliziing 5,100 0 x 3 ongi nna m n. 1r coo Ca S tree'cumng ""{Transverse (C) 41. 6 59. 0 n8 It canbe readily understood from Table I that the mechanical properties ofCa-S free-cutting steel are lower than those of Ca free-cutting steel,especially in that of the transverse direction (C). It was confirmedthrough many experiments that the reason for this degradation was use ofa higher S content in the Ca-S cutting steel.

The values which are depicted in the previously discussed and followingfigures were obtained with the same type cutting tools, depth of cut andcutting speed.

All of the machine structure steel, as shown in American Standards, i.e.A151 and the like, may be utilized as a basic starting point to whichthe other components of this inventive steel are added. The basic steelmay be selected from common carbon steels, heat resisting steels,chromium molybdenum steels, nickel chromium molyb denum steels or thelike. When each of the elements Ca.,

costs. Less than 0.005 of the same substantially reduces the abrasionamount to an undesirable degree.

Many experiments have been performed on the above steels. Typical steelsactually tested are shown in the below Table II. In this Table II,Charge No. 1 steel is based on known steel AISI-l045 and is regarded asa basic steel to which the other elements may be added in accordancewith this invention. Charge No. 2 steel is a Ca free-cutting steelproduced by adding Ca to the basic steel such as of Charge No. 1. ChargeNo. 3 steel is another Ca free-cutting steel. Charge No. 4 steel is aCa-S freecutting steel produced by adding S to the Ca free-cutting steelsuch as of Charge No. 2. Charge No. 5 steel is a Ca-Nb free-cuttingsteel produced by adding Nb to the Ca free-cutting steel such as ofCharge No. 2, but, the S01. Al. content is more than that of the presentinventive Sol. AL, and Nb and/ or V is added to each of the above steel.

TABLE II Chemical composition (percent) Charge number Components 0 SiMn' 8 S01. Al Cu Nb V 1 Basic steel 0. 41 0. 28 0. 68 0.022 2 Basicsteel Ca 0.42 0. 27 0. 65 0. 015 '4 d0 0. 45 0. 25 0. 63 0. 027 4 BasicSteel Ca S 0. 46 0. 18. 0.74 0. 060 6 Basic steel Ca Nb..... 0. 43 0. 280. 78 0. 029 6.. Basic steel Cu. V 0. 43 0. 32 0. 82 0. 021 7 BasicSteel Ca Nb... 0.43 0. 30 0. 74 0. 028 8 Basic steel Ca V-....- 0.45 0.27 0. 73 0. 028

steels, a new steel, which is the present inventive steel was produced.The inventive steel displays outstanding free-cutting properties andexcellent mechanical properties as a machine structure steel. It isreadily attained to perfection with ease and stability.

C, silicon (Si) and manganese (Mn) which are common elements in theabove steels should be within certain ranges. For example, C shouldpreferably range from 0.08% to 0.6%; Si should preferably range from0.15% to 0.60%; and Mn should preferably range from 0.30% to 2.00%. Morethan 0.6% C reduces the workability of steel and less than 0.08% C willsubstantially reduce the advantageous etfects of C as required in amachine structure steel, such as hardness. Si and Mn are useful fordeoxidation, and increasing yield strength and tensile strength of steelwith low cost. However, when the Si content is more than 0.6% or Mn ismore than 2.00%, the toughness of the steel is adversely affected.Conversely,

when the Si content is less than 0.15% or Mn is less than 0.30%, thesame above effects will be reduced substantially.

In the steel obtained with this invention, each of the elements, Ca,Sol. Al., and Nb and/or V, should be further added together with theabove-mentioned basic elements or other elements specified in thevariously used standards. The added ranges of Ca., Sol. Al., Nb. and V.are as follows: Ca is from 0.002% to 0.02%; Sol. Al. is from 0.005% to0.04%; and Nb. and/or V. is from 0.005% to 0.1%. When the Ca content ismore than 0.02%, workability of the resulting steel is reducedsubstantially and its cost increased, Conversely, less than 0.002% of Cawill Charge No. 6 steel is a Ca-V free-cutting steel produced by addingV to a Ca free-cutting steel such as of Charge No. 2, but with the S01.Al. content more than that of this invention. Charge No. 7 steel is aCa-Nb free-cutting steel produced in accordance with this invention.Charge No. 8 steel is a Ca-V free-cutting steel produced in accordancewith this invention.

The cutting requirements of the above samples were as follows:

cutting tool: A cemented carbide tool bit. cutting speed: m./min.

depth of cut: 2 mm.

feed: 0.25 nun/revolution.

Turning now to FIG. 6, there is depicted in graphic format, the abrasionproperties of a tool using the steel samples of Charges Nos. 1-8discussed above and shown in Table II. From FIG. 6, it can be readilyunderstood that the abrasion amount of a tool using the basic steel ofCharge No. l is large and for Ca free-cutting steel of Charges Nos. 2and 3, which were developed to improve the free-cutting properties ofbasic steel, abrasion amount is unstable. Charge No. 3 steel shows aconsiderable amount of abrasion as cutting time passes. The amount ofabrasion of Charge No. 2 steel is very small and is comparativelystable.

Ca-S free-cutting steel of Charge No. 4 was developed to stabilize thefree-cutting properties of Ca steel and is 6 restricted. The new steelsof this invention are not so restricted.

TABLE 111 Percent Yield Tensile Charge point, strength, Elon- Be-Heat-treatment and number Cut direction of test piece kg./mm. kg./mm.=gation duction test condition 1 {LongitudinalC(L) g3 23. g 52;. g g. g

giifiiiih i 1? .I 4214 691 a 2815 5015 850 c. x 30 min. air 2"{Transverse (C) 41. 5 69. 0 28. 0 51. 5 cooling (normaliz- Longitudinal(L) 40. 2 66. 6 29.4 52. 1 ing). Test piece; 4 "{Transverse (0).. 40.167.5 24. a 42. 5 Longitudinal, ns Longitudinal (L) 43. 0 69. 5 29. 5 51.8 No. 5, Transverse, 7 "{Transverse (0).- 42. 5 70.1 29. 0 so. 5 J18No.5. 8 {Longitudinal (L) 42. 8 70. 5 28. 5 50. 5 Transverse (C)- 41.968.9 29.3 49. 8

produced by the addition of sulphur. Referring again to FIG. 6, it canbe readily understood that the object of the Ca-S free-cutting steel hasbeen accomplished. The abrasion resistance of the tool using the Ca-Sfree-cutting steel is superior to Charge No. 2 steel and is stable,which was confirmed by other experiments, not shown herein. However, asmentioned above, there are deficiencies in the mechanical properties ofthe Ca-S free-cutting steel.

The steels produced in accordance with the principles of this inventionand shown as Charges Nos. 7 and 8 steels, have been developed to improveor eliminate the aforementioned deficiencies. Returning again to FIG.-6, the abrasion amount of a tool using the steel produced in accordancewith this invention is superior to that of the Ca-S free-cutting steelsand is also outstanding in stability, that is to say that the abrasiondepth does not change significantly with passage of time. At the sametime, as hereinafter mentioned the mechanical properties of each of thesteels produced using the principles of this invention are excellent andsubstantially better than those of the other above steels. In thisinvention the S01. Al. content is within a certain range; as well as theamount of each of the other elements Ca and Nb and/or V are within theabove discussed ranges.

The steel charges having Sol. Al. contents outside of the ranges of thisinvention are shown as comparative examples. These comparative samplesare Charges Nos. 5 and 6 Steel in FIG. 6. Referring to FIG. 6, it can bereadily understood that the abrasion resistance of a tool using steelshaving Sol. Al. contents more than 0.04% become substantially worse.

The mechanical properties of the steel shown in Table II are shown inTable III, given below. According to this Table III, it can be readilyunderstood that the mechanical properties of new steels produced inaccordance with this invention, namely Charges Nos. 7 and 8 steels, arefar superior to those of any of the other steels. At the same time itshould be noted that the mechanical properties of the Ca-S free-cuttingsteel Charges No. 4 steel, is clearly inferior to those of any of theother steels and especially inferior to a greater degree in elongation.Even though abrasion resistance of a tool using the Ca-S free-cuttingsteel is acceptable, as shown in FIG. 6, because of its inferiormechanical properties, its utility is substantially Turning now to FIG.7, there is depicted a graph showing the change of amount of abrasion ofa tool using the new steel produced according to the invention, with thepassage of cutting time, as compared with that of other typical steels.The graph data are the results of plotting data obtained through manyexperiments and samples. From the FIG. 7, it can be readily understoodthat the free-cutting properties of this invention has little dispersionand outstanding stability. The depth of abrasion does not increase inany significant amount with passage of cutting time.

Another example of this invention namely steel comprising Nb and Vtogether with the other above specified elements, is not shown in theabove tables. However, the results obtained with actual samples showedthat they are comparable with the results obtained with the separateaddition of Nb or V, provided that the added amounts of Nb and Vtogether is within the range as specified above.

Thus, it may be noted that the combination of the desired propertiesdiscussed above, which are required in the cutting work, has beenobtained by this invention for the first time.

While this invention was explained in terms of a preferred embodiment,various modifications and variations thereof would be evident to oneskilled in the art, and such modifications and variations are to beconsidered within the spirit and scope of this invention.

What is claimed is:

1. Steel composition consisting essentially of 0.002% to 0.02% Ca;0.005% to 0.04% sol. Al.; 0.005% to 0.1% Nb and/or V; 0.08% to 0.60% C;0.15% to 0.60% Si; 0.30% to 2.00% Mn and balance Fe and unavoidabletraces.

2. Composition of claim 1, wherein said element is Nb.

3. Composition of claim 1, wherein said element is V.

4. Composition of claim 1, wherein said element is Nb and V incombination.

References Cited UNITED STATES PATENTS 1,128,726 2/1915 Rubel 75-1242,687,954 8/ 1954 Lohr 75-124 3,155,495 11/1964 Nakamura 75-1243,357,822 12/1967 Miyoshi 75-124 HYLAND BIZOT, Primary Examiner

